The sacrament of baptism in an adult's life is one that should be treated with the utmost sanctity. Using a baptismal font for an adult may not provide the kind of experience desired. A full immersion baptism is often preferred. An indoor baptistry can be expensive to build and difficult to place in an existing structure. Constructing an outdoor baptistry is economical and can be accomplished in a weekend with some dedicated and able volunteers. Common pond heaters and pumps can keep the baptismal waters comfortable and clean.
Measure and mark out with spray paint a 5-foot by 10-foot rectangle on the ground where the baptistry will be located.
Hammer in a survey stake at each corner and run a string from each stake. Check that the rectangle is "squared" (each corner is 90 degrees) by measuring the diagonals between the two corners. Adjust the corner stakes and string until both diagonal measurements are equal.
Measure and mark out a line across the width of the rectangle 4 feet in from one edge and paint an "S" inside that small section.
Dig out the section that does not have an "S" with a shovel to the depth of 5 feet. Slope the sides down to the bottom so the top measurements of the hole will be 5 feet by 6 feet and the bottom will measure 4 feet by 5 feet (not including the "S" section).
Compact the earth with a hand tamper until it is smooth and hard.
Cut the section marked with "S" into a set of dirt stairs using a shovel to dig each step out so it is 8 inches wide and 8 inches tall. Make sure the first step starts 8 inches below the surface of the ground. Continue cutting the steps out and down from there. Compact the dirt steps using a hand tamper until they are smooth and hard.
Add 6 inches of pea gravel to the bottom of the baptistry to aide with groundwater drainage. Level the gravel by using the hand tamp.
Create a dry concrete mix by adding small amounts of water to dry concrete until the consistency is that of a very sticky dough---some of the stone in the mix should still be able to be seen.
Trowel the dry mix concrete over the entire surface of the baptistry, including the sides (a dry mix will "stack" and does not need vertical concrete forms). The concrete should be about 3 or 4 inches thick but does not have to be perfect.
Smooth over any areas with gaps that expose the stone in the concrete by dipping the trowel in water and troweling over the surface of the concrete. This will create a thin "wet mix" to seal any holes. Let the concrete set for 2 days.
Coat the concrete with epoxy pool paint following the manufacturer's instructions for application and drying time.
Fill the baptistry with water. Assemble and connect the pond pump/filter and heater by following the manufacturer's instructions.
Dig a small trench from where the pump/filter and heater will be placed to the electrical power source. The trench should be wide enough for the PVC pipe (that the electrical cord can run through) and it should be 6 to 12 inches deep. Pass the cord through the pipe and then bury the pipe. This will allow the cord to remain in place without creating a hazard or being damaged by the elements. Plug in everything.
Lay a tarp over the baptistry and drive camping stakes into the ground to cover it when not in use.